The Washington-area chamber chorus Voices 21 opens its 13th season with a festive holiday program featuring familiar carols — like “Deck the Halls” and “I Saw Three Ships”— and some with new arrangements; Renaissance motets by Cristóbal de Morales and Peter Philips; Egil Hovland’s “Stay With Us” and Morten Lauridsen’s mystical setting of “O Magnum Mysterium.” Make this a part of your annual holiday celebration.